Setup Graphical Logins

XDM

Then modify /etc/X11/xdm/Xaccess to allow any host to get
a login window. Look for a line that looks like this:

* #any host can get a login window

and remove the hash '#' sign at the beginning of the line.

In case you have multiple network interfaces also add a line like this:

LISTEN 192.168.0.10

Where 192.168.0.10 should be you server IP address.

Then reboot or restart your X server and xdm daemon.

GDM

Modify /etc/gdm/custom.conf to include:

[xdmcp]
Enable=true
Port=177

The restart the Gnome Display Manager:

systemctl restart gdm

Or if using the inittab method, login as root on another tty and

telinit 3
telinit 5 && exit

KDM

Edit kdmrc ( /opt/kde/share/config/kdm/kdmrc [KDE 3x] or /usr/share/config/kdm/kdmrc (KDE 4x] ) and at the end there should be something like this:

[Xdmcp]
Enable=true

Then you need to restart your X server so the change you just made takes effect:

systemctl restart kdm

SLiM

SLiM doesn't support Xdmcp.

Accessing X from a remote Machine on your LAN

You can access your login manager on the network computer 192.168.0.10 via the following command. TCP and UDP streams are opened. So it is not possible to access the login manager via an SSH connection.

Xnest -query 192.168.0.10 -geometry 1280x1024 :1

Or, with Xephyr, if you experience refreshing problems with Xnest:

Xephyr -query 192.168.0.10 -screen 1280x1024 -br -reset -terminate :1

Or, if you are on runlevel 3

X -query your_server_ip

Xserver should recognize your monitor and set appropriate resolution.

Note: You can enable XDMCP Direct/Query and Broadcast connections from remote hosts without XDM starting a local X server.

After allowing XDMCP access as described above, edit /etc/X11/xdm/Xservers and comment out:

Thin client setup

First of all one should setup dhcp and tftp server. Dnsmasq has both of them.
For network boot image check thinstation project.
If your network card does not support PXE, you can try Etherboot

Troubleshooting

XDMCP fatal error: Manager unwilling Host unwilling

This is usually caused by an entry missing from the /etc/kde3/kdm/Xaccess file. This file controls which machines can connect to the server via KDM. The trick is to add a line that starts with an asterisk '*'. Look for a line that looks like:

# * #any host can get a login window

and remove the hash '#' sign at the beginning of the line. Then, you need to restart KDM.

/etc/rc.d/kdm restart

Session declined: Maximum Number of Sessions Reached

Edit /etc/gdm/custom.conf and add/increase the maximum sessions.

[xdmcp]
Enable=true
MaxSessions=2

If you still cannot log in remotely

...and you see only a black screen, try removing the -nodaemon option in /etc/inittab to have only

x:5:respawn:/usr/sbin/gdm

Login screen and GNOME is somehow flickering

If the login screen is created again and again and unresponsive, you are trying to access GNOME Shell on the remote machine. This is apparently caused by network speed, e.g. by accessing via wireless connections. The workaround is to disable/deinstall GNOME Shell.